1. Field of the Invention
The invention relates to a working machine, in particular a tamper for ground-compaction purposes which is driven by means of an internal combustion engine, according to the preamble of claim 1.
2. Description of the Related Art
Tampers of this type are conventionally constructed in such a manner that an upper mass which accommodates a motor and a crank drive is connected by way of a spring set to a working mass which substantially forms a tamping plate. The crank drive converts the rotational movement, which is generated by the motor, into an oscillating linear movement, for which reason a guide piston is guided in such a manner as to be able to move longitudinally in a guide tube. The system which is located between the motor outlet and the tamping plate is defined hereinunder as the tamping system. In the case of modem tampers, the tamping system is provided with oil lubrication. In order to prevent oil from issuing out of the tamping system but also to prevent the penetration of dirt into the tamping system, the tamping system in the case of known tampers is surrounded by an enclosure which can consist, for example, of a combination of rigid housing parts and expansion bellows. To date, the enclosure has been designed in such a manner that it effects a complete seal of the tamping system which means that it is not possible to achieve pressure equalisation between the sealed interior and the atmosphere.
In the case of working machines of this type, for the purpose of lubricating the drive motor, i.e. the cylinder, the piston and the piston rings, as well as the bearings and the shaft sealing rings, it is conventional to provide a petroil lubrication, i.e. the operation with a fuel-oil mixture which is stored in liquid form in the tank. In order to configure the operation of these machines in the most convenient manner possible and with the lowest possible maintenance, the development is moving towards providing a separate lubrication, wherein the oil required to lubricate the motor is taken from the oil supply contained in the closed tamping system. Tests have shown that it is possible at this site to accommodate a sufficiently large quantity of oil without impairing the performance of the tamper. The desired switch to separate lubrication has hitherto been delayed because it has been assumed that to accomplish this it would be necessary to implement relatively large structural modifications on the machines introduced at that time, such as delivery devices for transporting the oil from the tamping system to the motor.